An estimated 1.3 million people in the US, especially women, suffer from rheumatoid arthritis (RA). Currently NSAIDs are used to relieve symptoms, and disease-modifying antirheumatic drugs (DMARDs) are used to produce remissions. However, these treatments are not satisfactory, prohibitively expensive (for protein based DMARDs), and often associated with potentially severe side effects. Biological understanding of the underline immune nature of RA accumulated in the last two decades have provided promises in using novel small molecules for better treatment of RA. We recently discovered that a novel class of vitamin D3 (VD3) metabolites, 20S-hydroxyvitamin D3 (20S(OH)D3), is highly efficacious against RA in vivo without resulting hypercalcemia or other detectable toxicities, even at very high doses. In this exploratory grant, we propose to test our overall hypothesis that the observed separation in strong efficacy against RA and the absence of hypercalcemia provided by this unique 20-hydroxy scaffold is due to the selective transcriptional activation of VDR in immune cells compared to intestine cells. This tissue selectivity, rather than the absolute potency of VDR activation, holds a new paradigm for developing clinically useful VD3 modulators for improved RA treatment. We have recently developed stereospecific synthetic methods to make new analogs. Some of these analogs show very promising anti-inflammation activities, at least comparable to that of 20S(OH)D3. Clearly there is room for further structural optimization based on 20S(OH)D3. Therefore, our objective is to develop several orally active, highly tissue-selective, VDR modulators based on this unique 20-hydroxyscaffold. Our specific aims are: (1) To test the hypothesis that the anti-inflammatory potency of 20S(OH)D3 can be further optimized with rational drug design. We will screen newly synthesized analogs against established markers for inflammation and use the structure-activity relationships (SAR) to guide iterative optimization for their anti-inflammatory activity. (2) To tst the hypothesis that the mechanism of action of the optimized highly active 20(OH)D3 analogs will selectively activate VDR in immune cells compared to intestine cells and that the in vitro selectivity observed will translate to in vivo efficacy for RA. We will test the hypotheses that (a they will activate VDR differentially in immune cells compared to intestine cells; (b) they will induce selective expression of key VDR- responsive genes in immune cells compared to intestine cells; (c) they will suppress RA efficiently without hypercalcemia using the well-established collagen induced arthritis (CIA) model. Our long term goal for this research is to develop novel classes of highly tissue-selective VDR modulators for immune cells compared to the intestine cells. Success in developing such agents will not only have high impact for RA, but will also have significant impact in treating many other autoimmune diseases.